default SMS source: sms_carriers option

[nqb]

sms_carriers option should include all the SMS carriers in DB.

It looks like the latest additions in DB haven't been added in conf/authentication.conf

[julsemaan]

Yeah this is because we reference the SMS carriers in authentication.conf as well.

We have 2 choices:

1. We adjust authentication.conf.example
2. We support making the sms_carriers empty and when its the case, it displays all the carriers in the DB

Would be cleaner to do option 2 and it would be future-proof

[nqb]

In option 2, admin can select SMS carriers in a dropdown list in the auth source.

However, if they don't, the default sms source will not work: guest can't select a provider which has not been defined in the source.

[julsemaan]

This is why we need to change the backend code to magically fill in all the carriers when the list is empty

[extrafu]

@nqb Please add manually the ones that are missing and open a PR.

[nqb]

For 8.3, I fixed missing sms_carriers in 7a1af6c